Cooling device and thermal treatment device

ABSTRACT

A cooling device cools a workpiece using a mist-like coolant and includes a heat transfer coefficient switching device that switches a heat transfer coefficient of the mist-like coolant from a relatively low state to a relatively high state during cooling the workpiece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application based on PCT PatentApplication No. PCT/JP2017/006551, filed on Feb. 22, 2017, whosepriority is claimed on Japanese Patent Application No. 2016-058930,filed on Mar. 23, 2016. The contents of both the PCT Patent Applicationand the Japanese Patent Application are incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates to a cooling device and a thermaltreatment device.

BACKGROUND ART

For example, Patent Document 1 discloses a quenching device. Thequenching device, when a mist-like coolant is blown onto a part heatedto a predetermined temperature so as to cool the part, lowers theatmospheric pressure before a temperature of the part exceeds amartensitic transformation temperature and lowers the boiling point ofthe coolant. According to the quenching device, a vapor film generatedbetween a surface of the part and a droplet of the coolant is maintainedby lowering the boiling point of the coolant, and thus, it is possibleto suppress distortion or deformation of the part.

CITATION LIST Patent Document

[Patent Document 1] Japanese Unexamined Patent Application, FirstPublication No. 2013-181226

SUMMARY Technical Problem

In the above-described quenching device, the distortion or thedeformation of the part is suppressed by maintaining the vapor film.However, complicated factors such as a shape of the part which is aworkpiece are involved in order to maintain the vapor film, and thus, itis difficult to stably maintain the vapor film by only lowering theboiling point of the coolant during a cooling period of the workpieceuntil the temperature of the workpiece exceeds the martensitictransformation temperature from a start of cooling. That is, it is notalways practical to maintain the vapor film so as to suppress thedistortion or the deformation of the part, and it is difficult toreliably suppress the distortion or the deformation of the workpiece.

The present disclosure is made in consideration of the above-describedcircumstances, and an object thereof is to reliably suppress thedeformation of the workpiece when the workpiece is cooled by themist-like coolant more than the related art.

Solution to Problem

In order to achieve the object, in the present disclosure, as a firstsolution, there is provided a cooling device which cools a workpieceusing a mist-like coolant, including: heat transfer coefficientswitching device that switches a heat transfer coefficient of themist-like coolant from a relatively low state to a relatively high stateduring cooling the workpiece.

According to the present disclosure, a technique for switching the heattransfer coefficient of the mist-like coolant from the relatively lowstate to the relatively high state during cooling the workpiece is used,and thus, it is possible to suppress the deformation of the workpiecemore reliably than the related art.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a first longitudinal sectional view showing an overallconfiguration of a cooling device and a multi-chamber thermal treatmentdevice according to an embodiment of the present disclosure.

FIG. 2 is a second longitudinal sectional view showing the overallconfiguration of the cooling device and the multi-chamber thermaltreatment device according to the embodiment of the present disclosure.

FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2.

FIG. 4 is a cross-sectional view taken along line B-B in FIG. 2.

FIG. 5A is a graph showing a temperature change of a cooling treatmentin the embodiment of the present disclosure.

FIG. 5B is a graph showing a change of mist particle diameters of amist-like coolant in the cooling treatment in the embodiment of thepresent disclosure.

FIG. 6 is a graph showing a thermal conductivity of each cooling medium.

FIG. 7 is a graph showing a relationship between an injection amount ofeach nozzle and a heat transfer coefficient in an experimental result ofthe present disclosure.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a cooling device R and a multi-chamber thermal treatmentdevice M according to an embodiment of the present disclosure will bedescribed with reference to the drawings.

As shown in FIG. 1, the multi-chamber thermal treatment device M is athermal treatment device in which the cooling device R, an intermediateconveyance device H, and three heating devices are integrated with eachother. In addition, FIG. 1 is a longitudinal sectional view at a centerposition in a horizontal direction of the intermediate conveyance deviceH, and in FIG. 1, two heating device among the three heating devices,that is, only a heating device K1 and a heating device K2 are shown.

The multi-chamber thermal treatment device M is a thermal treatmentdevice for performing a quenching treatment on a workpiece X. Theworkpiece X is various metal parts, and is a part which is formed of asteel material such as die steel (SKD material) or high-speed steel (SKHmaterial).

The cooling device R is a device for performing a cooling treatment onthe workpiece X, and as shown in FIGS. 1 to 4, includes a coolingchamber 1, a plurality of first and second cooling nozzles 2 a and 2 b(first and second injection nozzles), a plurality of mist headers 3, acooling pump 4, a heat exchanger 5, a cooling drain tube 6, a coolingwater tank 7, first and second control valves 8 a and 8 b, a coolingcontrol unit 9, or the like.

The plurality of mist headers 3, the cooling pump 4, the heat exchanger5, the cooling water tank 7, the first and second control valves 8 a and8 b, and the cooling control unit 9 configure a cooling supply device inthe present disclosure. Moreover, the coolant supply device and theplurality of first and second cooling nozzles 2 a and 2 b configure theheat transfer coefficient switching device in the present disclosure.

The cooling chamber 1 is a vertically cylindrical container (a containerwhose central axis is in a vertical direction) which accommodates theworkpiece X, and an internal space of the cooling chamber 1 is a coolingcompartment RS. The intermediate conveyance device H is provided on thecooling chamber 1. An opening through which the cooling compartment RScommunicates with the internal space (conveyance chamber HS) of theintermediate conveyance device H is formed in the cooling chamber 1. Theworkpiece X is loaded on or unloaded from the cooling compartment RSthrough the opening.

The plurality of first and second cooling nozzles 2 a and 2 b are thefirst and second injection nozzles which convert a predetermined coolantsupplied from the cooling pump 4 via the mist headers 3 and the heatexchanger 5 into a mist-like coolant to inject the mist-like coolant tothe workpiece X. Each of the first cooling nozzles 2 a is a firstinjection nozzle of an injection hole having a relatively small holediameter (first hole diameter) and each of the second cooling nozzles 2b is a second injection nozzle of an injection hole having a holediameter (second hole diameter) larger than that of the first coolingnozzle 2 a. That is, the particle diameter (first mist particlediameter) of the mist-like coolant injected from the first coolingnozzle 2 a is smaller than the particle diameter (second mist particlediameter) of the mist-like coolant injected from the second coolingnozzle 2 b. In addition, a supply destination of the coolant is switchedfrom the first injection nozzle (first cooling nozzle 2 a) to the secondinjection nozzle (second cooling nozzle 2 b), and thus, the mistparticle diameter of the mist-like coolant can be adjusted from thefirst mist particle diameter to the second mist particle diameter. Inaddition, the heat transfer coefficient switching device adjusts themist particle diameter of the mist-like coolant from a relatively smallparticle diameter to a relatively large particle diameter to switch theheat transfer coefficient of the mist-like coolant.

As shown in FIGS. 1 to 4, the plurality of first and second nozzles 2 aand 2 b are disposed so as to be distributed around the workpiece Xaccommodated in the cooling compartment RS. More specifically, theplurality of first and second cooling nozzles 2 a and 2 b are disposedto be distributed around the workpiece X such that the cooling nozzles 2a and 2 b surround the entire workpiece X and distances between thecooling nozzles 2 a and 2 b and the workpiece X are the same as eachother as possible in a state where the cooling nozzles 2 a and 2 b aredisposed in multiple stages (specifically, five stages) in the verticaldirection and are separated from each other at a predetermined intervalin a circumferential direction of the cooling chamber 1 (coolingcompartment RS).

In addition, the plurality of first and second cooling nozzles 2 a and 2b are grouped into a predetermined number. That is, the plurality offirst and second cooling nozzles 2 a and 2 b are grouped for each stagein the vertical direction of the cooling compartment RS and are alsogrouped in plural in the circumferential direction of the coolingchamber 1 (cooling compartment RS). As shown in FIGS. 3 and 4, the mistheader 3 is individually provided in each of a plurality of groups(nozzle groups).

More specifically, as shown in FIG. 1, the mist headers 3 are disposedin five stages in the vertical direction, and as shown in FIG. 3, twomist headers 3 are provided on the uppermost stage in an arc shape so asto surround the vicinity of the workpiece X. In addition, as shown inFIG. 4, three mist headers 3 are provided on each of four stages of thesecond stage from above to the lowermost stage, in an arc shape so as tosurround the vicinity of the workpiece X. Among the mist header 3 havingthe five-stage configuration, the plurality of second cooling nozzles 2b are provided on the mist headers 3 of the uppermost stage, the mistheaders 3 of the third stage from above, and the mist headers 3 of theuppermost stage, and in addition, the plurality of first cooling nozzles2 a are provided on the mist headers 3 of the second stage and thefourth stage from above. The plurality of first and second coolingnozzles 2 a and 2 b are adjusted such that a direction of each nozzleaxis faces a direction of the workpiece X and inject the coolantsupplied from the pump 4 via the mist headers 3 toward the workpiece X.

As shown in FIG. 1, the plurality of second cooling nozzles 2 bbelonging to the uppermost stage are disposed at a position higher thanan upper end of the workpiece X in the vertical direction. Meanwhile,the plurality of second cooling nozzles 2 b belonging to the lowermoststage are disposed at approximately the same height as that of a lowerend of the workpiece X. In addition, the plurality of second coolingnozzles 2 b belonging to the uppermost stage are disposed inside thefirst and second cooling nozzles 2 a and 2 b of other stages, that is,are disposed to be further separated from an inner surface of thecooling compartment RS than the first and second cooling stages 2 a and2 b of other stages.

Here, the coolant is a liquid having viscosity lower than a cooling oilwhich is generally used for cooling in the heat treatment, and forexample, is a water. The shape of each of the injection holes of theplurality of first and second cooling nozzles 2 a and 2 b is set suchthat the coolant such as a water is uniform at a predetermined injectionangle and becomes a droplet having a predetermined particle diameter. Inaddition, as shown in FIGS. 1 to 4, the injection angle of each of theplurality of first and second nozzles 2 a and 2 b and an intervalbetween the adjacent first and second cooling nozzles 2 a and 2 b areset such that droplets positioned on an outer peripheral side among thedroplets injected from the first and second cooling nozzles 2 a and 2 bintersect or collide with the droplets on the outer peripheral side fromthe adjacent first and second cooling nozzles 2 a and 2 b.

In addition, the plurality of first and second cooling nozzles 2 a and 2b inject the mist-like coolant to the workpiece X such that the entireworkpiece X is surrounded by aggregation of the droplets, that is, themist-like coolant. In the mist-like coolant, for example, the particlediameter of the droplet is 20 to 700 μm. Positions and angles of theplurality of first and second cooling nozzles 2 a and 2 b areappropriately set such that the mist-like coolant around the workpiece Xhas a uniform particle diameter and a uniform density.

The cooling device R of the present embodiment is a device for coolingthe workpiece X using the mist-like coolant, that is, is a device whichmist-cools the workpiece X. In addition, a cooling condition such as acooling temperature or a cooling time in the cooling device R isappropriately set according to an object of the heat treatment in theworkpiece X, a material of the workpiece X, or the like.

The plurality of mist headers 3 described above are an arc-shaped pipecommunicating with the plurality of first and second cooling nozzles 2 aand 2 b, and distribute the coolant taken in from a supply port to theplurality of first and second cooling nozzles 2 a and 2 b. In the mistheaders 3, the positions of the supply ports are set such that pressurelosses in the plurality of first and second cooling nozzles 2 a and 2 bare approximately the same as each other, and thus, the coolant isuniformly distributed to the plurality of first and second nozzles 2 aand 2 b.

Here, the heat transfer coefficient of the mist-like coolant injectedfrom the plurality of first and second nozzles 2 a and 2 b toward theworkpiece X is dependent on the particle diameter (mist particlediameter) of the mist-like coolant. In addition, the mist particlediameter is determined by the hole diameters (first and second holediameters) of the injection holes of the first and second coolingnozzles 2 a and 2 b. That is, the mist-like coolant having the firstmist particle diameter injected from the first cooling nozzle 2 a havingthe first hole diameter has a relatively small mist particle diameter,and thus, the heat transfer coefficient (first heat transfercoefficient) thereof is relatively low. Meanwhile, the mist-like coolanthaving the second mist particle diameter injected from the secondcooling nozzle 2 b having the second hole diameter has a mist particlediameter larger than the first mist particle diameter, and thus, theheat transfer coefficient (second heat transfer coefficient) thereof isrelatively low.

The cooling pump 4 pumps the coolant of the cooling water tank 7 to themist headers 3. The heat exchanger 5 is a temperature controller whichadjusts (maintains) the temperature of the coolant supplied from thecooling pump 4 to the mist headers 3 to a predetermined temperature,based on a temperature instruction input from the cooling control unit9. That is, the temperature of the coolant supplied from the coolingpump 4 to the mist headers 3 is controlled by the cooling control unit9.

The cooling drain tube 6 is a pipe which communicates with a lowerportion of the cooling chamber 1 and the cooling water tank 7, and adrain valve (not shown) is provided in an intermediate portion of thecooling drain tube 6. The cooling water tank 7 is a liquid container inwhich the coolant drained from the cooling chamber 1 via the coolingdrain tube 6 or a cooling circulation pipe (not shown) is stored. Inaddition, the cooling circulation pipe is a pipe which communicates withan upper portion of the cooling chamber 1 and an upper portion of thecooling water tank 7 in order to return the coolant which has flowedfrom the cooling chamber 1 to the cooling water tank 7 during immersioncooling.

The first and second valves 8 a and 8 b are an on-off valve which isprovided between the plurality of mist headers 3 and the heat exchanger5. In the first and second control valves 8 a and 8 b, the secondcontrol valve 8 b is provided between the mist header 3 of the uppermoststage, the third stage from above, and the lowermost stage in which thesecond cooling nozzles 2 b are provided and the heat exchanger 5, andthe first control valve 8 a is provided between the mist headers 3 ofthe second stage and fourth stage from above in which the first coolingnozzles 2 a are provided and the heat exchanger 5. That is, the firstcontrol valve 8 a switches supply/non-supply of the coolant to theplurality of first cooling nozzles 2 a, based on a first opening/closingsignal input from the cooling control unit 8. Meanwhile, the secondcontrol valve 8 b switches supply/non-supply of the coolant to theplurality of second cooling nozzles 2 b, based on a secondopening/closing signal input from the cooling control unit 8.

The cooling control unit 9 operates the heat exchanger 5, the first andsecond control valves 8 a and 8 b, the drain valve, or the likedescribed above to control all operations of the cooling device R. Aspart of the control of the cooling device R, the cooling control unit 9controls the first and second control valves 8 a and 8 b to switch thesupply/non-supply of the coolant to the plurality of first and secondcooling nozzles 2 a and 2 b. Accordingly, the heat transfer coefficientof the mist-like coolant during cooling the workpiece X is switched froma relatively low state to a relatively high state. In addition,switching processing of the heat transfer coefficient of the mist-likecoolant performed by the cooling control unit 9 will be described indetail.

The intermediate conveyance device H includes a conveyance chamber 10, aconveyance chamber placement table 11, a cooling compartmentlifting/lowering table 12, a cooling compartment lifting/loweringcylinder 13, a pair of conveyance rails 14, a pair of pusher cylinder(pusher cylinder 15 and pusher cylinder 16), a heating chamberlifting/lowering table 17, a heating chamber lifting/lowering cylinder18, or the like. The conveyance chamber 10 is a container which isprovided between the cooling device R and the three heating devicesincluding the heating device K1 and the heating device K2, and theinternal space of the conveyance chamber 10 is the conveyance chamberHS. The workpiece X is loaded into a conveyance chamber 10 from aload/unload opening (not shown) by an external conveyance device in astate of being accommodated in a container such as a basket.

The conveyance chamber placement table 11 is a support table whichblocks a delivery port between the cooling chamber 1 and the conveyancechamber 10 when the workpiece X is cooled by the cooling device R, andother workpieces X can be placed on the conveyance chamber placementtable 11. The cooling compartment lifting/lowering table 12 is a supporttable on which workpiece X is placed when the workpiece X is cooled bycooling device R, and supports the workpiece X so that a bottom portionof workpiece X is exposed as widely as possible. The cooling compartmentlifting/lowering table 12 is fixed to a tip of a movable rod of thecooling compartment lifting/lowering cylinder 13.

The cooling compartment lifting/lowering cylinder 13 is an actuatorwhich moves (lifts or lowers) the cooling compartment lifting/loweringtable 12 vertically. That is, the cooling compartment lifting/loweringcylinder 13 and the cooling compartment lifting/lowering table 12 are adedicated conveyance device of the cooling device R, and convey theworkpiece X placed on the cooling compartment lifting/lowering table 12from a conveyance chamber HS to the cooling compartment RS and conveysthe workpiece X from the cooling compartment RS to the conveyancechamber HS.

The pair of conveyance rails 14 is installed to extend horizontally on afloor portion in the conveyance chamber 10. The conveyance rails 14 area guide member for conveying the workpiece X between the cooling deviceR and the heating device K1. The pusher cylinder 15 is an actuator whichpresses the workpiece X when the workpiece X in the conveyance chamber10 is conveyed toward the heating device K1. The pusher cylinder 16 isan actuator which presses the workpiece X when the workpiece X isconveyed from the heating device K1 to the cooling device R.

That is, the pair of conveyance rails 14, the pusher cylinder 15 and thepusher cylinder 16 are a dedicated conveyance device which conveys theworkpiece X between the heating device K1 and the cooling device R.Moreover, in FIG. 1, the pair of conveyance rails 14, the pushercylinder 15, and the pusher cylinder 16 are shown. However, an actualintermediate conveyance device H includes three pairs of conveyancerails 14, the pusher cylinder 15, and the pusher cylinder 16. That is,the conveyance rails 14, the pusher cylinder 15, and the pusher cylinder16 are used not only for the heating device K1 but also for the othertwo heating devices.

The heating chamber lifting/lowering table 17 is a support table onwhich the workpiece X is placed when the workpiece X is conveyed fromthe intermediate conveyance device H to the heating device K1. That is,the workpiece X is pressed in a right direction in FIG. 1 by the pushercylinder 15, and thus, the workpiece X is conveyed immediately on theheating chamber lifting/lowering table 17. The heating chamberlifting/lowering cylinder 18 is an actuator which moves (lifts orlowers) the workpiece X on the heating chamber lifting/lowering table 17vertically. That is, the heating chamber lifting/lowering table 17 andthe heating chamber lifting/lowering cylinder 18 are a dedicatedconveyance device of the heating device K1, and conveys the workpiece Xplaced on the heating chamber lifting/lowering table 17 from theconveyance chamber HS to the inner portion (heating chamber KS) of theheating device K1 and conveys the workpiece X from the heating chamberKS to the conveyance chamber HS.

The three heating devices have substantially the same configuration aseach other, and thus, in the following descriptions, the configurationof the heating device K1 will be described as a representative. Theheating device K1 includes a heating chamber 20, a heat-insulatingcontainer 21, a plurality of heaters 22, a vacuum vent tube 23, a vacuumpump 24, a stirring blade 25, a stirring motor 26, or the like.

The heating chamber 20 is a container which is provided on theconveyance chamber 10, and the internal space of the heating chamber 20is the heating chamber KS. Similarly to the above-described coolingchamber 1, the heating chamber 20 is a vertically cylindrical container(a container in which a central axis thereof is in the verticaldirection). However, the heating chamber 20 is formed to be smaller thanthe cooling chamber 1. The heat-insulating container 21 is a verticallycylindrical container provided in the heating chamber 20, and is formedof a heat-insulating material having predetermined heat-insulatingproperties.

The plurality of heaters 22 are a rod-shaped heating element and areprovided at a predetermined interval in the circumferential directioninside the heat-insulating container 21 in a vertical posture. Theplurality of heaters 22 heats the workpiece X accommodated in theheating chamber KS to a desired temperature (heating temperature). Inaddition, a heating condition such as a heating temperature or a heatingtime is appropriately set according to an object of the heat treatmentin the workpiece X, a material of the workpiece X, or the like.

Here, the heating condition includes a degree of vacuum (pressure) ofthe heating chamber KS. The vacuum vent tube 23 is a pipe whichcommunicates with the heating chamber KS, and one end of the vacuum venttube 23 is connected to an upper portion of the heat-insulatingcontainer 21 and the other end thereof is connected to the vacuum pump24. The vacuum pump 24 is a vent pump which sucks air in the heatingchamber KS via the vacuum vent tube 23. The degree of vacuum in theheating chamber KS is determined by a vent amount of air by the vacuumpump 24.

The stirring blade 25 is a rotating blade which is provided on the upperportion in the heat-insulating container 21 in a posture in which adirection of a rotary shaft thereof is the vertical direction (up-downdirection). The stirring blade 25 is driven by the stirring motor 26 andstirs air in the heating chamber KS. The stirring motor 26 is a rotationdrive source which is provided on the heating chamber 20 such that anoutput shaft thereof is in the vertical direction (up-down direction).The output shaft of the stirring motor 26 positioned on the heatingchamber 20 is connected to the rotary shaft of the stirring blade 25positioned in the heating chamber 20 so as not to damage airtightness(sealing properties) of the heating chamber 20.

In addition, the multi-chamber thermal treatment device M according tothe present embodiment includes a control panel (not shown). Thiscontrol panel includes an operation unit to which various conditions inthe heat treatment are set and input by a user, and a control unit whichoperates the cooling device R, the intermediate conveyance device H, andthe three heating devices in cooperation with each other, based onvarious conditions input from the operation unit and a control programstored in advance. That is, in the multi-chamber thermal treatmentdevice M, the cooling device R, the intermediate conveyance device H,and the three heating devices are automatically controlled by thecontrol panel, and thus, a quenching treatment is performed on theworkpiece X.

Here, the above-described cooling control unit 8 is a functionalcomponent responsible for the cooling control of the workpiece Xperformed by the cooling device R, among the control functions of thecontrol panel. That is, the control pane performs a conveyance controlof the workpiece X by the intermediate conveyance device H and a heatingcontrol of the workpiece X by the three heating devices in addition tothe cooling control of the workpiece X by the cooling device R.

Next, the operation (quenching treatment) of the multi-chamber thermaltreatment device M according to the present embodiment will be describedin detail with reference to FIGS. 5A and 5B.

In the quenching treatment by multi-chamber thermal treatment device M,after the workpiece X is heated to a predetermined temperature T1(heating temperature), first cooling (rapid cooling) is performed on theworkpiece X to a temperature T2 (cooling temperature), and thereafter,second cooling is performed on the workpiece X to a martensitetransformation temperature. When the quenching treatment of theworkpiece X is performed, the workpiece X is accommodated into theintermediate conveyance device H from the load/unload opening by aworker. In addition, if the load/unload opening is closed by the workerand the inside of the conveyance chamber HS is an enclosed space, theintermediate conveyance device H operates the pusher cylinder 15 tomoves the workpiece X onto the heating chamber lifting/lowering table17. In addition, the heating chamber lifting/lowering cylinder 18 isoperated by the intermediate conveyance device H, and thus, theworkpiece X is accommodated in the heating chamber KS of the heatingdevice K1.

In addition, if the workpiece X is accommodated in the heating chamberKS, the heating device K1 operates the heater 22 to heat the workpiece Xto the temperature T1. In addition, if the heating is completed, theintermediate conveyance device H operates the heating chamberlifting/lowering cylinder 18 and the pusher cylinder 16 to move theworkpiece X onto the cooling compartment lifting/lowering table 12. Inaddition, the intermediate conveyance device H operates the coolingcompartment lifting/lowering cylinder 13 to move the workpiece X to thecooling compartment RS, and a delivery port between the conveyancechamber 10 and the cooling chamber 1 is blocked by the conveyancechamber placement table 11. In addition, the cooling device R operatethe cooling pump 4 to inject the mist-like coolant from the plurality offirst and second cooling nozzles 2 a and 2 b toward the workpiece X. Asa result, the workpiece X is subjected to primary cooling (mist cooling)from the temperature T1 to the temperature T2.

In the primary cooling (mist cooling), as shown in FIG. 5A, theworkpiece X at the temperature T1, that is, the workpiece X having theaustenitic structure is rapidly cooled so as to reach the temperature T2avoiding a pearlite-structure-transformation point Ps (so-calledpearlite nose). That is, the workpiece X is rapidly cooled from thetemperature T1 to the temperature T2 by injection of the mist-likecoolant from the plurality of first and second cooling nozzles 2 a and 2b during a time t1 to a time t2 in FIG. 5A. In FIG. 5A, a surfacetemperature history of the workpiece X is indicated by a solid line andan internal temperature history of the workpiece X is indicated by abroken line.

Here, in the primary cooling (mist cooling) in the present embodiment,at a time ta which is an intermediate time between the time t1 and thetime t2, switching of the heat transfer coefficient of the mist-likecoolant from the relatively low state to the relatively high state isperformed once. That is, in a period (early cooling period S1) from thetime t1 to the time ta, the cooling control unit 9 sets the firstcontrol valve 8 a to an open stage and sets the second control valve 8 bto a closed state, and as shown in FIG. 5B, the mist-like coolant havinga first particle diameter C1 is injected from the first cooling nozzles2 a toward the workpiece X. That is, in the early cooling period S1, theworkpiece X is cooled by the mist-like coolant having the first heattransfer coefficient.

Moreover, in a period (late cooling period S2) from the time ta to thetime t2, the cooling control unit 8 sets the first control valve 8 a tothe closed state and sets the second control valve 8 b to the openstate, that is, the supply destination of the coolant is switched fromthe first cooling nozzle 2 a to the second cooling nozzle 2 b, and thus,as shown in FIG. 5B, the mist-like coolant having a second mist particlediameter C2 is injected from the second cooling nozzle 2 b toward theworkpiece X. That is, in the late cooling period S2, the workpiece X iscooled by the mist-like coolant having the second heat transfercoefficient higher than the first heat transfer coefficient of the earlycooling period S1.

Here, the first heat transfer coefficient of the mist-like coolant inthe early cooling period S1, that is, the first mist particle diameterC1 is set so as to maximally suppress the deformation of the workpiece Xcaused by the primary cooling (mist cooling). That is, the first mistparticle diameter C1 is determined for each material and shape of theworkpiece X by an experiment or the like which is performed in advance.In addition, the early cooling period S1, that is, the time to is alsodetermined for each material and shape of the workpiece X by anexperiment or the like which is performed in advance.

As described in Background Art, in the mist cooling, the vapor filmcannot be maintained, and thus, the part (workpiece) is deformed.However, in the present embodiment, the vapor film is not maintained.That is, the heat transfer coefficient of the mist-like coolant islowered by the setting the first particle diameter C1 in ahigh-temperature period of the workpiece X in which the workpiece X isdeformed, that is, in the early cooling period S1. In addition, as aresult, the deformation of the workpiece X is suppressed by suppressingcooling efficiency with respect to the workpiece X.

In the mist cooling with respect to the workpiece X in the early coolingperiod S1, a decrease in the temperature of the workpiece X becomesrelatively gentle. Accordingly, in a case where, similarly to the earlycooling period S1, the mist cooling is performed by the mist-likecoolant having the first mist particle diameter C1 in the late coolingperiod S2, it may be impossible to avoid thepearlite-structure-transformation point Ps in the primary cooling.Accordingly, in the present embodiment, the mist cooling is performed inthe late cooling period S2 by the mist-like coolant having the secondmist particle diameter C2 which is the particle diameter larger than thefirst mist particle diameter C1. Accordingly, the cooling efficiency inthe late cooling period S2 is improved compared to the coolingefficiency in the early cooling period S1, the primary cooling in whichthe pearlite-structure-transformation point is avoided is realized.

Here, as shown in FIG. 6, from data of a cooling curve of a silvercolumn specimen (10 mm in diameter, 30 mm in length) quenched in arepresentative cooling agent such as tap water, oil (JIS NipponIndustrial Standard C 2320-1999 Type 1 No. 2 oil), and nitrogen (10 bar15 m/s), surface heat transfer characteristic curves of each coolingagent calculated by a concentrated heat capacity method are known.

According to FIG. 6, in a high-temperature region in which a surfacetemperature of the silver column specimen is 600° C. or more, it isunderstood that a surface heat transfer coefficient of the tap water of30° C. is larger than that of the oil of 80° C.

Accordingly, for example, a mist cooling experiment using water as themist-like coolant of a test piece (workpiece) was performed using thefollowing cooling device simulating the above embodiment.

The cooling device included a water tank, a predetermined pipe, and anozzle.

The water tank had a capacity of 60 L, and water used for cooling wasstored in the water tank. In addition, the water tank was pressurized bynitrogen gas and was connected to the predetermined pipe.

Two types of nozzles including a one-fluid nozzle which ejects onlywater and a two-fluid nozzle that ejects fine particles of water usinggas was adopted as a nozzle. More specifically, ¼M JJXP 060 HTPVCmanufactured by Ikeuchi Co., Ltd. was used for one-fluid nozzle 1-1,¼KSFHS 0865 manufactured by Everloy Co., Ltd. was used for one-fluidnozzle 1-3, M¼ EX 438 manufactured by Niikura Kogyo Co., Ltd was usedfor one-fluid nozzle 1-4, and ¼ KSAMF 1875-¼ A24 ¼ W20 manufactured byEverloy Co., Ltd. was used for two-fluid nozzle 2-2. In addition, thenozzle was provided on an end portion opposite to an end portion of thepredetermined pipe to which the water tank was attached. Moreover, a tipof the nozzle was positioned at a position separated by 200 mm from thesurface of the test piece.

For the test piece, a disc-shaped stainless steel (JIS JapaneseIndustrial Standard SUS 304) having a thickness of 50 mm and a diameterof 100 mm was used. The test piece was inserted into an electric furnaceand heated to 1000° C.

The water stored in the water tank was pressurized by the nitrogen gas,and the pressurized water was injected to the test piece heated to 1000°C. In addition, the water was injected from each nozzle such that theinjection liquid pressure was 0.03 to 0.5 MPa.

Next, a temperature measurement method will be described.

Thermocouples were installed at six locations in total including fourlocations of 2 mm, 6 mm, 10 mm, and 25 mm in the depth direction fromthe surface at a center position of the test piece and two locationsshifted from each other by 180° in a circumferential direction at aposition of 25 mm from the upper end and 2 mm from the surface on a sidesurface of the test piece.

In addition, the test piece heated to 1000° C. was subjected to mistcooling and a temperature change of the test piece was measured untilthe temperature of the test piece became a normal temperature.

FIG. 7 shows a result of performing the mist cooling test andcalculating an average heat transfer coefficient from the time change ofthe temperature of the thermocouple inserted in the test piece. Inaddition, FIG. 7 shows the average heat transfer coefficient in a casewhere the surface temperature of the test piece corresponds to a rangeof 600 to 1000° C.

A dotted line in FIG. 7 shows a value in a case where oil cooling isperformed, and if the nozzle of 1-3 which was the one-fluid nozzle orthe nozzle of 2-2 which was the two-fluid nozzle was used, even in themist cooling in which water was used, the heat transfer coefficientwhich was approximately the same as that of the cooling oil wasrealized. That is, according to the cooling device using the mistcooling, the heat transfer coefficient of the mist-like coolant can belowered to be approximately the same as that of the cooling oil. Inaddition, it is possible to suppress the deformation of the workpiece Xby suppressing the cooling efficiency of the workpiece X.

As described above, according to the cooling device R of the presentembodiment, the mist particle diameter of the mist-like coolant isadjusted from the first mist particle diameter C1 to the second mistparticle diameter C2 between the period in which the workpiece X has arelatively high temperature, that is, the early cooling period S1, andthe period in which the workpiece X has a relatively low temperature,that is, the late cooling period S2. Therefore, the deformation of theworkpiece X in the primary cooling is suppressed, and it is possible toavoid the perlite-structure-transformation point Ps.

In addition, the present disclosure is not limited to theabove-described embodiment. For example, the following modificationexamples are considered.

(1) As shown in FIG. 5B, in the above-described embodiment, the mistparticle diameter of the mist-like coolant is adjusted from the secondmist particle diameter C1 to the first mist particle diameter C2, andthus, the heat transfer coefficient of the mist-like coolant is switchedfrom the first heat transfer coefficient to the second heat transfercoefficient. However, the present disclosure is not limited to this. Thedensity (mist density) of the mist-like coolant may be switched so as toswitch the thermal conductivity from the first heat transfer coefficientto the second heat transfer coefficient. For example, the density of themist-like coolant may be adjusted from a relatively low density to arelatively high density so as to switch the heat transfer coefficient ofthe mist-like coolant.

For example, a gas-liquid two-phase flow of including a coolant and apredetermined gas is injected to the workpiece X from the injectionnozzle as the mist-like coolant, a mixing ratio of the gas to thecoolant is adjusted such that a mist density is adjusted from a firstmist density to the second mist density, and thus, the heat transfercoefficient is switched from the first heat transfer coefficient to thesecond heat transfer coefficient. In addition, instead of adjusting themist density, the mist density may be switched by adjusting a flow rateof the coolant supplied to the injection nozzle.

(2) In the above-described embodiment, as shown in FIG. 5B, the firstmist particle diameter C1 and the second mist particle diameter C2 areswitched at the time ta. However, the present disclosure is not limitedto this. For example, the mist-like coolant having the first mistparticle diameter C1 and the mist-like coolant having the second mistparticle diameter C2 may be injected from the first and second coolingnozzles 2 a and 2 b over a predetermined period (overlap period) fromtime ta, and after the overlap period, only the mist-like coolant havingthe second mist particle diameter C2 may be injected from the secondcooling nozzle 2 b.

That is, the mist particle diameter of the mist-like coolant may beadjusted from the first mist particle diameter to the second mistparticle diameter via a state where the mist-like coolant having thefirst mist particle diameter and the mist-like coolant having the secondmist particle diameter are mixed with each other.

The overlap period is a period in which the mist-like coolant having thefirst mist particle diameter C1 and the mist-like coolant having thesecond mist particle diameter C2 coexist. That is, the overlap period isa period in which a mist-like coolant having a heat transfer coefficientin the middle of the first heat transfer coefficient and the second heattransfer coefficient exists. The mist particle diameter of the mist-likecoolant is adjusted from the first mist particle diameter C1 to thesecond mist particle diameter C2 through the overlap period, and thus,the switching from the first heat transfer coefficient to the secondheat transfer coefficient can be gently performed. Therefore, accordingto the above-described configuration, it is possible to suppressaccumulation of thermal stress in the workpiece X.

(3) In the above-described embodiment, the mist-like coolant having thefirst mist particle diameter C1 is injected in the early cooling periodS1, and the mist-like coolant having the second mist particle diameterC2 is injected in the late cooling period S2. However, the disclosure isnot limited to this. In the late cooling period S2, in addition to themist-like coolant having the second mist particle diameter C2, themist-like coolant having the first mist particle diameter C1 may beinjected. In this case, not only the mist particle diameter increasesand the heat transfer coefficient increases but also the mist densitycan be increased, and thus, the heat transfer coefficient can be furtherincreased.

(4) As shown in FIG. 1, in the above-described embodiment, themulti-chamber thermal treatment device M (thermal treatment device) inwhich the cooling device R, the intermediate conveyance device H, andthe three heating devices are integrated with each other is described.However, the present disclosure is not limited to this. The minimumconfiguration device of the thermal treatment apparatus is the heatingdevice and the cooling device. That is, the heat treatment apparatus maybe provided with the heating device for heating the workpiece and thecooling device for cooling the workpiece heated by the heating device.Therefore, a conveyance device such as an intermediate conveyance devicemay be separate from the thermal treating device.

INDUSTRIAL APPLICABILITY

According to the cooling device and the thermal treatment device of thepresent disclosure, the technique for switching the heat transfercoefficient of the mist-like coolant from the relatively low state tothe relatively high state during cooling the workpiece is used, andthus, it is possible to suppress the deformation of the workpiece morereliably than the related art.

What is claimed is:
 1. A cooling device which cools a workpiece using amist-like coolant, comprising: a heat transfer coefficient switchingdevice that switches a heat transfer coefficient of the mist-likecoolant from a relatively low state to a relatively high state duringcooling the workpiece.
 2. The cooling device according to claim 1,wherein the heat transfer coefficient switching device adjusts a mistparticle diameter of the mist-like coolant from a relatively smallparticle diameter to a relatively large particle diameter to switch theheat transfer coefficient of the mist-like coolant.
 3. The coolingdevice according to claim 2, wherein the heat transfer coefficientswitching device includes, a first injection nozzle that includes aninjection hole having a first hole diameter and converts a coolant intothe mist-like coolant having a first mist particle diameter of arelatively small mist particle diameter, a second injection nozzle thatincludes an injection hole having a second hole diameter larger than thefirst hole diameter and converts the coolant into the mist-like coolanthaving a second mist particle diameter larger than the first mistparticle diameter, and a coolant supply device that supplies the coolantto the first injection nozzle and the second injection nozzle, andwherein a supply destination of the coolant is switched from the firstinjection nozzle to the second injection nozzle to adjust the mistparticle diameter of the mist-like coolant from the first mist particlediameter to the second mist particle diameter.
 4. The cooling deviceaccording to claim 2, wherein the heat transfer coefficient switchingdevice adjusts the mist particle diameter of the mist-like coolant froma first mist particle diameter to a second mist particle diameter via astate where the mist-like coolant having the first mist particlediameter and the mist-like coolant having the second mist particlediameter are mixed.
 5. The cooling device according to claim 3, whereinthe heat transfer coefficient switching device adjusts the mist particlediameter of the mist-like coolant from the first mist particle diameterto the second mist particle diameter via a state where the mist-likecoolant having the first mist particle diameter and the mist-likecoolant having the second mist particle diameter are mixed.
 6. Thecooling device according to claim 1, wherein the heat transfercoefficient switching device adjusts a density of the mist-like coolantfrom a relatively low density to a relatively high density to switch theheat transfer coefficient of the mist-like coolant.
 7. A thermaltreatment device, comprising: a heating device that heats a workpiece;and the cooling device according to claim 1 that cools the workpieceheated by the heating device.
 8. A thermal treatment device, comprising:a heating device that heats a workpiece; and the cooling deviceaccording to claim 2 that cools the workpiece heated by the heatingdevice.
 9. A thermal treatment device, comprising: a heating device thatheats a workpiece; and the cooling device according to claim 3 thatcools the workpiece heated by the heating device.
 10. A thermaltreatment device, comprising: a heating device that heats a workpiece;and the cooling device according to claim 4 that cools the workpieceheated by the heating device.
 11. A thermal treatment device,comprising: a heating device that heats a workpiece; and the coolingdevice according to claim 5 that cools the workpiece heated by theheating device.
 12. A thermal treatment device, comprising: a heatingdevice that heats a workpiece; and the cooling device according to claim6 that cools the workpiece heated by the heating device.